Laser irradiation apparatus

ABSTRACT

An apparatus for irradiating an irradiation surface with a laser light having a linear or rectangular shape. A homogenizer operates on the principle that variations in the light intensity profile of an original beam as emitted from a laser device are dispersed by passing the original beam through two multi-cylindrical lenses. The directions of the respective multi-cylindrical lenses are set so as not to be parallel with the beam movement direction. Thus, an uniformity of annealing by irradiating with a laser light is improved.

RELATED APPLICATION INFORMATION

This application is a continuation of U.S. application Ser. No.09/036,005 filed Mar. 4, 1998, now U.S. Pat. No. 5,959,779.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus to be used for anannealing or exposure process including laser light irradiation. Forexample, the invention relates to an apparatus that provides a uniformirradiation effect in a laser annealing apparatus in which irradiationwith a large-area beam is performed. This type of laser annealingapparatus is used for semiconductor manufacturing processes.

2. Description of the Related Art

The technique of crystallizing an amorphous silicon film by irradiationwith laser light is known. Further, the technique of irradiating asilicon film that has been damaged by implantation of impurity ions torecover its crystallinity and to activate implanted impurity ions isalso known. They are called laser annealing techniques.

A typical example of the latter technique is a technique for annealingthe source and drain regions of a thin-film transistor. In thistechnique, the source and drain regions are annealed by laser lightirradiation after implanting impurity ions such as phosphorus or boronions into those regions.

Such a process with laser light irradiation has a feature that asubstrate receives almost no thermal damage.

This feature decreases limitations on materials to be processed andprovides an advantage in, for instance, forming a semiconductor deviceon a substrate such a glass substrate that is low in heat resistance. Inparticular, this feature is important in manufacturing an active matrixliquid crystal display device whose application range has expanded inrecent years.

In the active matrix liquid crystal display device, it is desired to usea glass substrate due to requirements of cost reduction and increase inarea.

The glass substrate cannot withstand a heat treatment at as high atemperature as more than 600° C. or even more than 700° C. Theabove-mentioned technique of crystallizing an amorphous silicon film orperforming annealing after implantation of impurity ions by laser lightirradiation is effective in avoiding this problem.

In the method of using laser light irradiation, even a glass substratereceives almost no thermal damage. As a result, a thin-film transistorusing a crystalline silicon film can be formed even with the use of aglass substrate.

However, in general, laser light as generated from a lasing device(hereinafter referred to as “original beam”) is small in beam area.Therefore, a common method of processing a large subject area is to scanit with laser light, which however has such problems as a longprocessing time and low uniformity in the effect of process in thesubject area. In particular, because of a non-uniform light intensityprofile, an ordinary original beam causes very poor uniformity in theeffect of processing if it is used as it is.

In view of the above, various techniques have been proposed which modifyan original beam so as to obtain a beam that is as uniform as possibleand even a beam that is changed in size and shape so as to conform tothe size, shape, etc. of a surface or region to be irradiated. Thecommon shapes of a resulting beam are a rectangular shape and a linearshape. According to these techniques, uniform laser annealing can beperformed over a large area.

FIG. 1 shows an example of a laser irradiation apparatus for modifyingan original beam. In FIG. 1, a laser oscillator 1 is an excimer laser,for instance. The excimer laser 1 oscillates to emit laser light byestablishing an excited state called an excimer state by decomposing apredetermined gas by high-frequency discharge.

For example, the KrF excimer laser produces excited states KrF* byhigh-voltage discharge by using material gases of Kr and F. Althoughthis excited state has a life of several nanoseconds to severalmicroseconds and hence is not stable, corresponding ground states KrF iseven less stable. An inverted distribution is thereby produced in whichthe density of excited states is higher than that of ground states. Thiscauses stimulated emission and laser light can be produced at relativelyhigh efficiency.

It goes without saying that the laser oscillator 1 is not limited to anexcimer laser and may be a pulsed laser or a CW laser. In general, thepulsed laser is suitable for the purpose of obtaining a high energydensity.

An original beam emitted from the laser oscillator 1 is modified into aproper size by a concave lens 2 and a convex lens 3. FIG. 1 shows a casewhere the original beam is enlarged in the vertical direction. The beamat this stage is still called an original beam because its lightintensity is equivalent to that of the state immediately after theemission from the laser oscillator 1.

The original beam then enters an optical device called a homogenizer,which includes at least two lens devices (each called amulti-cylindrical lens, a lenticular lens or a flyeye lens) 4 and 5 eachhaving a large number of cylindrical lenses. In general, themulti-cylindrical lenses 4 and 5 are disposed orthogonally as shown inthe insert view in FIG. 1.

The number of multi-cylindrical lenses may be one or three or more.Where only one multi-cylindrical lens is provided, the non-uniformity ofthe original beam in one direction is dispersed. Where two or moremulti-cylindrical lenses are disposed so as to be orientated in the samedirection, the same effect as would be obtained by increasing the numberof constituent cylindrical lenses can be obtained.

By causing the original beam to pass through the homogenizer, a highlyuniform beams with dispersed energy density can be obtained. Theprinciple and the problems of the homogenizer will be described later.The beam is then modified into an intended shape by various kinds oflenses 6, 7, and 9, changed in direction by a mirror 8, and finallyapplied to a sample (see FIG. 1).

Next, the principle and the problems, which is to be solved by theinvention, of the homogenizer will be described. To avoid complexity, inthe following an optical discussion will be given to only one surface.Laser light that has passed through a multi-cylindrical lens is as shownin FIG. 2A.

In FIG. 2A, L is a multi-cylindrical lens including three constituentcylindrical lenses, and a laser light (an original beam) entering eachcylindrical lens is refracted by it. The beams diffuse after beingconverged at focuses F₁-F₃. There occurs a mixing region where all ofthe light beams that have passed through the respective cylindricallenses are mixed with each other.

Now assume that the original beam has a deviation in its light intensityprofile and hence the beams entering the respective cylindrical lenseshave different light intensities. However, the deviation is dispersed inthe mixing region because the beams that have passed through therespective cylindrical lenses are mixed with each other there. The lightintensity is thus uniformized and a beam having a less varied lightintensity profile can be obtained (see FIG. 2A).

Incidentally, if attention is paid to the optical paths after thepassage through the multi-cylindrical lens, it is understood that thebeams are regarded as being emitted from point light sources F₁-F₃ thatare arranged at regular intervals. Further, since the original beam iscoherent, the beams emitted from the respective point light sources alsohave equal phases and hence interfere with each other. That is, portionswhere the beams cancel out each other (nodes) and portions where thebeams intensify each other (antinodes) occur depending on the distance xbetween the irradiation surface and the point light sources F₁-F₃ andthe interval 2 a between the point light sources F₁-F₃ (see FIG. 2B).

Contrary to the intended purpose, this means that the multi-cylindricallens introduce a new version of non-uniformity to the light intensityprofile. The positions of nodes and antinodes can be determined strictlyin a case where the number of point light sources is as small as two orthree. However, in an ordinary homogenizer the number of constituentcylindrical lenses is five or more (typically 10 to 30), in which casetaking into account all interferences among many point light sources isno more than cumbersome and does not constitute an essential discussion.Therefore, a consideration will be given below to interference at atypical antinode position.

Where two point light sources exist, an antinode is formed at a positionthat is equally distant from the point light source irrespective of thedistance x (see FIG. 3A). That is, where point light sources F₁ and F⁻¹exist, a relationship {overscore (F₁+L A)}={overscore (F⁻¹+L A)} holdsat point A on an irradiation surface. Irrespective of the interval 2 abetween the point light sources F₁ and F⁻¹ and the distance x, beamscoming from the point light sources F₁ and F⁻¹ have the same phase andhence intensify each other.

A consideration will now be given to a case where an additional pointlight source F⁻² exists (see FIG. 3B). In this case, a condition to besatisfied for beams coming from the point light source F⁻² and the otherpoint light sources F₁ and F⁻¹ to have the same phase and intensify eachother is such that an optical path difference {overscore (F⁻²+LA)}−{overscore (F⁻¹+L A)} be equal to an integral multiple nλ of thewavelength, which condition depends on the parameters a and x. That is,

{overscore (F⁻¹A+L )}−{overscore (F ⁻² A+L )}=nλ

should be satisfied.

Since a relationship a<<x usually holds, a simple calculation leads to

{overscore (F⁻¹A+L )}−{overscore (F ⁻² A+L )}=4a ² /x=nλ.

The same discussion applies to a point light source F₂ that is locatedat a position that is symmetrical to the position of the point lightsource F⁻² with respect to the broken line passing through point A.

Next, a consideration will be given to a case where additional pointlight sources F₂, F₃, F₄, F⁻³, . . . exist. In this case, as shown inFIG. 3C, optical path differences {overscore (F₃+L A)}−{overscore (F₂+LA)} and F₄A−F₃A satisfy

{overscore (F₃A+L )}−{overscore (F ₂ A+L )}=2(4a ² /x)=2nλ

{overscore (F₄A+L )}−{overscore (F ₃ A+L )}=3(4a ² /x)=3nλ.

More generally, as shown in FIG. 7A, as for an m-th (as counted frompoint A) point light source F_(m) and an (m+1)-th point light sourceF_(m+1), an optical path difference {overscore (F_(m+1)+L A)}−{overscore(F_(m)+L A)} satisfies

{overscore (F_(m+1)A+L )}−{overscore (F _(m) A+L )}=4ma ² /x.

Considering the relationship

4a ² /x=nλ,

we obtain the following equation:

{overscore (F_(m+1)A+L )}−{overscore (F _(m) A+L )}=4ma ² /x=mnλ.

That is, if a light beam coming from the point light source F₂ has thesame phase as a light beam coming from the point light source F₁, beamscoming from the other point light sources F₃, F₄, . . . , F_(m),F_(m+1), . . . also have the same phase and intensify each other (thebeams coming from all the point light sources have the same phase andintensify each other).

The intensify of a light beam coming from a point light source is ininverse proportion to the distance from it. However, since the abovediscussion assumes the relationship a<<x which means that the distancesbetween point A and the respective point light sources are approximatelythe same, a conclusion is obtained that the beams from all the pointlight sources intensify each other approximately equally. Lightintensity I at point A is given by I=Ni, where i is the intensity of alight beam coming from each point light source and N is the number ofpoint light sources.

A consideration will now be given to a condition to be satisfied for alight beam coming from the point light source F⁻² to cancel out, atpoint A, a light beam coming from the point light source F⁻¹. Thisoccurs when those beams have an optical path difference that is equal tothe half wavelength multiplied by an odd integer. That is,

{overscore (F⁻¹A+L )}−{overscore (F ⁻² A+L )}=4a ² /x=(n+½)λ

should be satisfied (see FIG. 4A).

When this condition is satisfied, beams coming from the point lightsources F₁ and F⁻¹ are canceled out by an opposite-phase light beamcoming from the point light source F⁻² and light intensity I at point Ais given by I=2i−i=i.

Where another point light source F₂ exists as shown in FIG. 4B, since alight beam coming from the point light source F₂ also has a phaseopposite to that of a light beam coming from the point light source F₁,the light intensity at point A becomes 0.

Next, a consideration will be given to point light sources F₃ and F₄. Asshown in FIG. 4C, optical path differences {overscore (F₃+LA)}−{overscore (F₂+L A)} and {overscore (F₄+L A)}−{overscore (F₃+L A)}satisfy

{overscore (F₃A+L )}−{overscore (F ₂ A+L )}=2(4a ² /x)=(2n+1)λ

{overscore (F₄A+L )}−{overscore (F ₃ A+L )}=3(4a ² /x)=(3n+1+½)λ.

That is, a light beam coming from the point light source F₃ has the samephase as a light beam coming from the point light source F₂ (i.e., ithas a phase opposite to that of a light beam coming from the point lightsource F₁), and a light beam coming from the point light source F₄ has aphase opposite to that of a light beam coming from the point lightsource F₃ (i.e., it has the same phase as the light beam coming from thepoint light source F₁) (see FIG. 4C).

More generally, as for an m-th (as counted from point A) point lightsource F_(m) and an (m+1)-th point light source F_(m+1), an optical pathdifference {overscore (F_(m+1)+L A)}−{overscore (F_(m)+L A)} satisfies

{overscore (F_(m+1)A+L )}−{overscore (F _(m) A+L )}=4ma ² /x=m(n+½)λ.

Now, a consideration will be given to the phases of beams coming frompoint light sources F_(m) with respect to the phase of the light beamcoming from the point light source F₁.

 {overscore (F₂A+L )}−{overscore (F ₁ A+L )}=(n+½)λ

{overscore (F₃A+L )}−{overscore (F ₂ A+L )}=(2n+1)λ

{overscore (F₄A+L )}−{overscore (F ₃ A+L )}=(3n+{fraction (3/2)})λ

{overscore (F_(m)A+L )}−{overscore (F _(m−1) A+L )}=(m−1)(n+½)λ

Summing up the above equations, we obtain

(left side)={overscore (F_(m)A+L )}−{overscore (F ₁ A+L )}

(right side)={m(m−1)}(n+½)λ÷2.

Where m=4, 5, 8, 9, . . . , 4k, 4k+1, . . . , the optical pathdifference {overscore (F_(m)+L A)}−{overscore (F₁+L A)} is calculated as

{overscore (F_(m)A+L )}−{overscore (F ₁ A+L )}=k(4k−1)(2n+1)λ(m=4k)

or

{overscore (F_(m)A+L )}−{overscore (F ₁ A+L )}=4k ²(4n+2)λ(m=4k+1).

Therefore, a light beam coming from the point light source F_(m) has thesame phase as that coming from the point light source F₁. In the othercases, the light beam coming from the point light source F_(m) has aphase opposite to that of the light beam coming from the point lightsource F₁.

Although the phase relationship is complex as described above, the lightintensity I at point A varies between 0 and 2i and is anywaysufficiently smaller than that in the case of FIGS. 3A-3C.

Discussions similar to the above can be made with respect to point Bthat is the foot of the perpendicular from each point light source tothe irradiation surface. Point B is a point closest to a certain pointlight source F₀ in the irradiation surface. Consider a case whereadditional point light sources F₁ and F⁻¹ exist adjacent to the pointlight source F₀. In this case, a relationship

{overscore (F₁B+L )}={overscore (F ⁻¹ B+L )}

naturally holds, which means beams coming from the point light sourcesF₁ and F⁻¹ intensify each other irrespective of a, x, and λ.

If {overscore (F₁+L B)}−{overscore (F₀+L B)}=nλ, a light beam comingfrom the point light source F₀ also has the same phase as that comingfrom the point light source F₁ at point B and hence the light intensityI at point B is given by I=3i. In this case, a relationship 2a²/x=nλholds (see FIG. 5A).

On the other hand, if {overscore (F₁+L B)}−{overscore (F₀+L B)}=(n+½)λ,the light beam coming from the point light source F₀ has a phaseopposite to that of the light beam coming from the point light source F₁at point B and hence the light beams offset each other so that the lightintensity I at point B is given by I=i. In this case, a relationship2a²/x=(n+½)λ holds (see FIG. 6A).

Next, a consideration will be given to a case where additional pointlight sources F₂, F⁻², F₃, F⁻³, . . . exist. Where the condition of FIG.5A is satisfied, relationships

{overscore (F₂B+L )}−{overscore (F ₁ B+L )}=3(2a ² /x)=3nλ

{overscore (F₃B+L )}−{overscore (F ₂ B+L )}=5(2a ² /x)=5nλ

hold (see FIG. 5B).

More generally, as shown in FIG. 7B, as for an m-th (as counted frompoint B) point light source F_(m) and an (m+1)-th point light sourceF_(m+1), an optical path difference {overscore (F_(m+1)+L B)}−{overscore(F_(m)+L B)} satisfies

{overscore (F_(m+1)B+L )}−{overscore (F _(m) B+L )}=2(2m+1)a ²/x=(2m+1)λ.

That is, if the light beam coming from the point light source F₁ has thesame phase as that coming from the point light source F₀, beams comingfrom the point light sources F₂, F₃, . . . , F_(m), F_(m+1), . . . alsohave the same phase and intensify each other (the beams coming from allthe point light sources have the same phase and intensify each other).The light intensity I at point B is given by I=Ni where N is the numberof point light sources.

On the other hand, where the condition of FIG. 6A is satisfied,relationships

{overscore (F₂B+L )}−{overscore (F ₁ B+L )}=(3n+1+½)λ

{overscore (F₃B+L )}−{overscore (F ₂ B+L )}=(5n+2+½)λ

hold (see FIG. 6B). That is, a light beam coming from the point lightsource F₂ has a phase opposite to that of a light beam coming from thepoint light source F₁ (the former has the same phase as a light beamcoming from the point light source F₀). A light beam coming from thepoint light source F₃ has a phase opposite to that of the light beamcoming from the point light source F₂ (the former has the same phase asa light beam coming from the point light source F₁).

More generally, the following relationships hold:

{overscore (F₁B+L )}−{overscore (F ₀ B+L )}=(n+½)λ

{overscore (F₂B+L )}−{overscore (F ₁ B+L )}=3(n+½)λ

{overscore (F₃B+L )}−{overscore (F ₂ B+L )}=5(n+1)λ

{overscore (F_(m)B+L )}−{overscore (F _(m−1) B+L )}=(2m+1)(n+½)λ.

Summing up the above equations, we obtain

(left side)={overscore (F_(m)B+L )}−{overscore (F ₀ B+L )}

(right side)={m(m+2)}(n+½)λ.

That is, where m is an odd number (2k), the optical path difference{overscore (F_(m)+L B)}−{overscore (F₀+L B)} is calculated as

{overscore (F_(m)B+L )}−{overscore (F ₀ B+L )}=2k(k+1)(2n+1)λ.

Therefore, a light beam coming from the point light source F_(m) has thesame phase as that coming from the point light source F₀. In the othercases, the light beam coming from the point light source F_(m) has aphase opposite to that of the light beam coming from the point lightsource F₀.

Although the phase relationship is complex as described above, the lightintensity I at point B varies between 0 and 2i and is anywaysufficiently smaller than in the case of FIGS. 5A and 5B.

In the above examples, the interference conditions, at each of thepeculiar points A and B, of beams coming from a plurality of point lightsources were determined. The number of points equivalent to points A andB is approximately equal to the number of point light sources (i.e., thenumber of constituent cylindrical lenses). At points A and B, the lightintensity is very high or close to 0 depending on the values of a, x,and λ.

For example, if a=1 mm, x=1 m=10³ mm, and λ=0.25 μm=0.25×10⁻³ mm, thelight intensity at point A corresponds to the case of FIGS. 3A-3C (beamsintensify each other) when x=970 mm, corresponds to the case of FIGS.4A-4C (beams cancel out each other) when x=985 mm, again corresponds tothe case of FIGS. 3A-3C when x=1,000 mm, and so forth. The interferencestates drastically vary every time the distance x between themulti-cylindrical lens to the irradiation surface is changed by 15 mm.

At point B, the intensity varies at a cycle that is a half of the abovecycle (7.5 mm).

Satisfying the condition of FIGS. 5A and 5B, i.e., 2a²/x=nλ, means thatthe condition of FIGS. 3A-3C is also satisfied; both of points A and Bare antinodes. However, the condition of FIGS. 5A and 5B is not alwayssatisfied even if the condition of FIGS. 3A-3C is satisfied.

Similarly, satisfying the condition of FIGS. 6A and 6B, i.e.,2a²/x=(n+½)λ, is equivalent to satisfying the condition of FIGS. 4A-4C;points A and B become an antinode and a node, respectively. However, thecondition of FIGS. 6A and 6B is not always satisfied even if thecondition of FIGS. 4A-4C is satisfied.

In this manner, each of points A and B becomes a node in some case andan antinode in another case. Now assume a case where a certain conditionis satisfied and antinodes appear on an irradiation surface. Wheremulti-cylindrical lenses are arranged orthogonally as in the case ofFIG. 1, beams intensify each other at portions where antinodes intersecteach other and dot-like antinodes (i.e., portions of high lightintensity) thereby appear in a regular manner as shown in FIG. 8A.

Th expanse of each of the above dot-like antinodes varies depending onthe condition satisfied, and in a certain situation part or all of theabove dot-like antinodes may turn to nodes.

If beams are modified into linear shapes, that is, if they arecompressed (reduced) in a beam movement direction (scanning direction)and expanded in the direction perpendicular to the beam movementdirection, a light intensity profile as shown in FIG. 8B appears inwhich the light intensity is unduly high at the antinodes and close to 0at the nodes. Defects are prone to occur at the portions of these twotypes when the irradiated sample is subjected to annealing. Inparticular, the problem is serious if variations in light intensity aresteep.

Two problems arise when laser annealing is performed by using beams asdescribed above. The first problem is non-uniformity caused by overlapof beam spots. This is because in applying laser light while moving itthe next beam (beam spot-2 in FIG. 8C) is applied so as to overlap witha first beam (beam spot-1). Practically it is impossible to performirradiation without causing overlap of beams. However, it is possible tosufficiently reduce the influences of the overlap by optimizing theenergy density and the number of pulses applied.

On the other hand, the problem of non-uniformity of a beam that iscaused through interference according to the above-described principleis more serious. As shown in FIG. 8D, defects that are caused by thenon-uniformity of a beam through interference occur in dotted form in asingle beam spot. Further, defects-1 caused by the beam spot-1 anddefects-2 caused by the beam spot-2 are located on the same lines, whichresults from the fact that the beam movement direction is parallel withthe direction of at least one of the multi-cylindrical lenses. In thecase of a linear beam, this results from the fact that the longitudinaldirection of the beam is perpendicular to the direction of at least oneof the multi-cylindrical lenses.

The term “direction of a multi-cylindrical lens” as used above means thedirection of straight lines that are formed at the focuses by light thatis output from the multi-cylindrical lens. That is, in FIG. 2A, thedirection of the multi-cylindrical lens is the direction perpendicularto the paper surface. Further, the term “beam movement direction” is ahigher-rank concept and does not simply mean a spatial movementdirection, because in ordinary laser annealing apparatuses the opticalpath is changed several times by mirrors in a path from a homogenizer toan irradiation surface.

Thus, when a substrate is processed by a conventional laser annealingapparatus, there occur defects arranged perpendicularly to the beammovement direction and defects arranged parallel with it as shown inFIG. 8D. The former is linear defects due to overlap of beams and thelatter is defects due to non-uniformity in light intensity that iscaused by interference.

In particular, defects arranged in the horizontal and verticaldirections are fatal to matrix devices (for instance, active matrixcircuits and memory circuits) because defects occur on a certain row orcolumn and hence are easy to find. In a liquid crystal display device,these defects are particularly problematic when driver circuits are alsoformed on the substrate.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems in theart, and an object of the invention is therefore to improve theuniformity of annealing that is performed by irradiation with laserlight.

According to a first aspect of the invention, the beam movementdirection is not set parallel with the direction of any ofmulti-cylindrical lenses. According to a second aspect of the invention,in the case of using a linear beam, the longitudinal direction of thebeam is not set perpendicular to the direction of any ofmulti-cylindrical lenses.

The concept of the invention will be described below with reference toFIGS. 9A-9E. For example, consider a homogenizer having twomulti-cylindrical lenses 4 and 5 as shown in FIG. 1. Conventionally, thedirection of the multi-cylindrical lens 4 is perpendicular to the beammovement direction as shown in FIG. 9B. On the other hand, the directionof the multi-cylindrical lens 5 is parallel with the beam movementdirection. (Double-headed arrows indicate the directions of therespective multi-cylindrical lenses 4 and 5.)

This type of configuration has the problems as described above. Incontrast, the invention provides, for instance, a configuration in whichalthough the multi-cylindrical lens 4 is disposed in the same directionas in the conventional case, the multi-cylindrical lens 5 is inclined soas not to be parallel with the beam movement direction (see FIG. 9A).This configuration satisfies the requirement of the invention that noneof the directions of the multi-cylindrical lenses are parallel with thebeam movement direction.

With the homogenizer having the above configuration, dot-like defects(defects-1 and defects-2) due to non-uniformity that is caused byinterference appear obliquely with respect to the beam movementdirection as shown in FIG. 9C. In general, there is no inevitabilitythat defects-1 and defects-2 occur on the same lines. Therefore, nolinear defects are formed.

However, attention should be paid to a special case in which defects-1and defects-2 occur on the same lines. This corresponds to a case wherethe distance d between the top of a certain one of straight linesrepresenting dot-like defects (see FIG. 9D) and the bottom of some otherstraight line is 0. In this case, dot-like defects are alignedobliquely.

This problem occurs not only between adjacent straight lines but alsoother apart lines: it is necessary to prevent the distance d frombecoming 0 even in the case of FIG. 9E.

However, particularly in the case of matrices, since dot-like defects onoblique straight lines are not parallel with the rows and columns of amatrix, they seldom constitute apparent linear defects.

The above discussion also applies in completely the same manner even ifthe term “beam movement direction” is replaced by another term“direction perpendicular to the longitudinal direction, i.e., theshorter-axis direction (of a linear beam).” The direction of themulti-cylindrical lens 4 need not be perpendicular to the beam movementdirection; it is sufficient that the direction of the multi-cylindricallens 4 be not parallel with the beam movement direction. Therefore, aconfiguration according to the invention can be obtained simply byrotating, around the optical axis of laser light, a homogenizer that hastwo orthogonal multi-cylindrical lenses like the conventionalhomogenizer, and can provide the advantages of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an optical system of a conventional laserirradiation apparatus;

FIGS. 2A and 2B schematically show optical paths of a multi-cylindricallens and a resulting interference of the prior art;

FIGS. 3A-3C to FIGS. 6A-6B illustrate interference conditions ofcoherent light beams coming from a plurality of point light sources ofthe prior art;

FIGS. 7A-7B show calculation formulae of optical path differences oflight beams coming from a plurality of point light sources of the priorart;

FIGS. 8A-8D illustrate how a conventional beam causes defects and howthe defects are arranged, etc., of the prior art;

FIGS. 9A, 9C-9E illustrate configurations of multi-cylindrical lensesaccording to the invention, manners how defects occur, etc., and FIG. 9Billustrate a configuration of conventional multi-cylindrical lenses,manners how defects occur, etc.; and

FIG. 10 schematically shows an optical system of a laser irradiationapparatus according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

An optical system according to this embodiment will be described below.The basic configuration of a laser irradiation apparatus according tothis embodiment is the same as that shown in FIG. 1 except an anglearound the optical axis of the multi-cylindrical lenses of thehomogenizer. An original beam before entering the homogenizer has arectangular shape of 6 cm×5 cm. The following description will beconcentrated on the homogenizer.

In the configuration of this embodiment, the multi-cylindrical lens 5 iscomposed of 12 cylindrical lenses each being 5 mm in width and dividesincident laser light into about 10 parts.

In this embodiment, a linear laser beam that is finally applied has alongitudinal length of 12 cm. The direction of the multi-cylindricallens 5 is set so as to form 45° with the beam movement direction. On theother hand, the direction of the multi-cylindrical lens 4 is setperpendicular to the beam movement direction (see FIG. 9A).

The width of a beam that is output from the homogenizer is reduced, bythe downstream optical system, by a factor of {fraction (1/25)} into 0.2cm in the beam movement direction and enlarged by a factor of 2 into 12cm in the direction perpendicular to the beam movement direction,whereby a linear beam is obtained.

Embodiment 2

FIG. 10 schematically shows a configuration according to thisembodiment.

In this embodiment, rectangular laser light 801 output from a laseroscillator (not shown) is passed through or reflected bymulti-cylindrical lenses 802 and 803, cylindrical lenses 804 and 805, amirror 806, and a cylindrical lens 807, whereby it is shaped into linearlaser light, which is finally applied to an irradiation surface.

The configuration of FIG. 10 has a feature that the twomulti-cylindrical lenses 802 and 803 are inclined by 45° from the beammovement direction and the longitudinal direction of the beam. (That is,the multi-cylindrical lenses 802 and 803 are located orthogonally eachother.)

Although two multi-cylindrical lenses are used in this embodiment, threeor more multi-cylindrical lenses may be used.

As described above, the invention provides a technique capable ofperforming uniform annealing over a large area in laser irradiationprocesses that are used for manufacture of semiconductor devices, forinstance.

What is claimed is:
 1. A method of irradiating with a laser light havinga linear or rectangular shape, said method comprising the steps of:scanning with the laser light in a scanning direction, wherein the laserlight is generated by a laser irradiation apparatus, wherein the laserirradiation apparatus comprising: a homogenizer including at least onemulti-cylindrical lens; a plurality of cylindrical lenses in themulti-cylindrical lens, wherein a direction of the multi-cylindricallens is not parallel with the scanning direction.
 2. A method accordingto claim 1, wherein the homogenizer includes at least twomulti-cylindrical lenses, and wherein the multi-cylindrical lenses arelocated perpendicular to each other.
 3. A method according to claim 1,wherein the direction of the multi-cylindrical lens is defined as adirection of straight lines being formed at focuses by the laser lightwhich outputs from the multi-cylindrical lens.
 4. A method according toclaim 1, wherein the homogenizer includes at least two multi-cylindricallenses, and wherein one of the multi-cylindrical lenses makes an angleof 45° with respect the other of the multi-cylindrical lenses.
 5. Amethod of irradiating with a laser light having a linear or rectangularshape, wherein the laser light is generated by a laser irradiationapparatus, wherein the laser irradiation apparatus comprising: ahomogenizer including at least one multi-cylindrical lens; a pluralityof cylindrical lenses in the multi-cylindrical lens, wherein a directionof the multi-cylindrical lens is not perpendicular to a longitudinaldirection of the laser light.
 6. A method according to claim 5, whereinthe homogenizer includes at least two multi-cylindrical lenses, andwherein the multi-cylindrical lenses are located perpendicular to eachother.
 7. A method according to claim 5, wherein the direction of themulti-cylindrical lens is defined as a direction of straight lines beingformed at focuses by the laser light which outputs from themulti-cylindrical lens.
 8. A method according to claim 5, wherein thehomogenizer includes at least two multi-cylindrical lenses, and whereinone of the multi-cylindrical lenses makes an angle of 45° with respectthe other of the multi-cylindrical lenses.
 9. A method of fabricating asemiconductor device, said method comprising the steps of: generating alaser light having a linear or rectangular shape by a laser irradiationapparatus, wherein the laser irradiation apparatus comprising: ahomogenizer including at least one multi-cylindrical lens; a pluralityof cylindrical lenses in the multi-cylindrical lens, scanning with thelaser light in the scanning direction, wherein a direction of themulti-cylindrical lens is not parallel with the scanning direction. 10.A method according to claim 9, wherein the homogenizer includes at leasttwo multi-cylindrical lenses, and wherein the multi-cylindrical lensesare located perpendicular to each other.
 11. A method according to claim9, wherein the direction of the multi-cylindrical lens is defined as adirection of straight lines being formed at focuses by the laser lightwhich outputs from the multi-cylindrical lens.
 12. A method according toclaim 9, wherein the homogenizer includes at least two multi-cylindricallenses, and wherein one of the multi-cylindrical lenses makes an angleof 45° with respect the other of the multi-cylindrical lenses.
 13. Amethod according to claim 9, wherein the semiconductor device is a thinfilm transistor.
 14. A method according to claim 9, wherein thesemiconductor device is an active matrix display device.
 15. A methodaccording to claim 9, wherein the semiconductor device is an activematrix type liquid crystal display device.
 16. A method of fabricating asemiconductor device including a semiconductor film, said methodcomprising the steps of: generating a laser light having a linear orrectangular shape by a laser irradiation apparatus, wherein the laserirradiation apparatus comprising: a homogenizer including at least onemulti-cylindrical lens; a plurality of cylindrical lenses in themulti-cylindrical lens, crystallizing the semiconductor film by scanningwith the laser light in a scanning direction, wherein a direction of themulti-cylindrical lens is not parallel with the scanning direction. 17.A method according to claim 16, wherein the homogenizer includes atleast two multi-cylindrical lenses, and wherein the multi-cylindricallenses are located perpendicular to each other.
 18. A method accordingto claim 16, wherein the direction of the multi-cylindrical lens isdefined as a direction of straight lines being formed at focuses by thelaser light which outputs from the multi-cylindrical lens.
 19. A methodaccording to claim 16, wherein the homogenizer includes at least twomulti-cylindrical lenses, and wherein one of the multi-cylindricallenses makes an angle of 45° with respect the other of themulti-cylindrical lenses.
 20. A method according to claim 16, whereinthe semiconductor device is a thin film transistor.
 21. A methodaccording to claim 16, wherein the semiconductor device is an activematrix display device.
 22. A method according to claim 16, wherein thesemiconductor device is an active matrix type liquid crystal displaydevice.
 23. A method of fabricating a semiconductor device, said methodcomprising the steps of: generating a laser light having a linear orrectangular shape by a laser irradiation apparatus, wherein the laserirradiation apparatus comprising: a homogenizer including at least onemulti-cylindrical lens; a plurality of cylindrical lenses in themulti-cylindrical lens, wherein a direction of the multi-cylindricallens is not perpendicular to a longitudinal direction of the laserlight, annealing with the laser light.
 24. A method according to claim23, wherein the homogenizer includes at least two multi-cylindricallenses, and wherein the multi-cylindrical lenses are locatedperpendicular to each other.
 25. A method according to claim 23, whereinthe direction of the multi-cylindrical lens is defined as a direction ofstraight lines being formed at focuses by the laser light which outputsfrom the multi-cylindrical lens.
 26. A method according to claim 23,wherein the homogenizer includes at least two multi-cylindrical lenses,and wherein one of the multi-cylindrical lenses makes an angle of 45°with respect the other of the multi-cylindrical lenses.
 27. A methodaccording to claim 23, wherein the semiconductor device is a thin filmtransistor.
 28. A method according to claim 23, wherein thesemiconductor device is an active matrix display device.
 29. A methodaccording to claim 23, wherein the semiconductor device is an activematrix type liquid crystal display device.
 30. A method of fabricating asemiconductor device including semiconductor film, said methodcomprising the steps of: generating a laser light having a linear orrectangular shape by a laser irradiation apparatus, wherein the laserirradiation apparatus comprising: a homogenizer including at least onemulti-cylindrical lens; a plurality of cylindrical lenses in themulti-cylindrical lens, wherein a direction of the multi-cylindricallens is not perpendicular to a longitudinal direction of the laserlight, crystallizing the semiconductor film by irradiating with thelaser light.
 31. A method according to claim 30, wherein the homogenizerincludes at least two multi-cylindrical lenses, and wherein themulti-cylindrical lenses are located perpendicular to each other.
 32. Amethod according to claim 30, wherein the direction of themulti-cylindrical lens is defined as a direction of straight lines beingformed at focuses by the laser light which outputs from themulti-cylindrical lens.
 33. A method according to claim 30, wherein thehomogenizer includes at least two multi-cylindrical lenses, and whereinone of the multi-cylindrical lenses makes an angle of 45° with respectthe other of the multi-cylindrical lenses.
 34. A method according toclaim 30, wherein the semiconductor device is a thin film transistor.35. A method according to claim 30, wherein the semiconductor device isan active matrix display device.
 36. A method according to claim 30,wherein the semiconductor device is an active matrix type liquid crystaldisplay device.